Scientists Investigate Why Bird Flu’s Impact Varies Across Species

Researchers are trying to understand why bird flu, known as H5N1, kills some animals quickly while causing only moderate illness in others. The virus has killed millions of wild and domestic birds worldwide and has also infected seals, cats, dogs, and cows. as reported by PBS.

H5N1 has largely stayed out of the human population, but the World Health Organization (WHO) reported that as of April 1, 2024, it had caused nearly 900 human infections and 463 deaths since 2003. Most human cases involved direct contact with infected birds, with human-to-human transmission occurring only with close and extended contact within households.

The current strain of bird flu, first identified in 1959, did not cause significant concern until an outbreak in Hong Kong in 1997 led to severe sickness and deaths in humans. Scientists continue to study why H5N1 has not heavily affected humans, though they remain cautious about future mutations.

Dr. Tom Frieden, former director of the U.S. Centers for Disease Control and Prevention (CDC) and head of the non-profit Resolve to Save Lives, emphasized the need for vigilance. “There’s a lot we don’t understand,” Frieden told The Associated Press. “I think we have to get over the ‘hope for the best and bury our head in the sand’ approach.” told by Voice of America.

Some researchers suggest flu viruses originating in birds have caused severe human pandemics in the past, such as those in 1918 and 1957. While many experts believe it is unlikely that the current virus will become a deadly global pandemic, U.S. health officials are preparing vaccines as a precaution. At present, no other measures are planned since the virus is not causing severe disease in humans and there is no strong evidence of person-to-person transmission.

The U.S. Department of Agriculture has reported outbreaks among dairy cows and over 1,000 groups of poultry in the U.S. At least four human infections have been reported among the hundreds of thousands of people working at poultry and dairy farms. Globally, 15 human infections from the current virus strain have been identified, including one death in southern China in 2022. Most cases exhibited mild or no symptoms.

Experts are investigating whether humans may have built up some immunity from other virus forms or vaccinations. However, a study of human blood samples suggested there is little to no existing immunity to this bird flu strain.